The invention relates to systems for displaying images, and more particularly, to micro-reflective transmission liquid crystal displays.
Liquid crystal displays (LCDs) are widely used in information displays. Generally, liquid crystal displays (LCDs) comprise a liquid crystal panel assembly including two substrates provided with two kinds of field generating electrodes such as pixel electrodes and a common electrode and a liquid crystal layer with dielectric anisotropy interposed therebetween. The variation of the voltage difference between the field generating electrodes, i.e., the variation in the strength of an electric field generated by the electrodes, changes the transmittance of the light passing through the LCD, and desired images are thus obtained by controlling the voltage difference between the electrodes.
The conventional three primary color LCD comprises a plurality of pixels with pixel electrodes and red (R), green (G) and blue (B) color filters. Each pixel is separately driven to perform display operation by way of the signals applied thereto through display signal lines. The signal lines include gate lines (or scanning signal lines) for carrying the scanning signals, and data lines for carrying data signals. Each pixel has a thin film transistor (TFT) connected to one of the gate lines and one of the data lines to control the data signals applied to the pixel electrode. However, the conventional three primary color LCDs have poor optical efficiency which may be eliminated by adding a white pixel spacer to set the three RGB color pixels apart in a transmissive LCD device.
FIG. 1A shows the spatial arrangement of four color RGBW pixels of a conventional LCD. The conventional four color LCD 10 includes a plurality of pixel regions of red (RP), green (GP), blue (BP), and white (WP). The white pixel (WP) may have no color filter. FIG. 1B is a cross-section of an arrangement of a conventional micro-reflective transmission display. A micro-reflective transmission liquid crystal display 100 comprises a liquid crystal panel assembly including a lower substrate 11 provided with storage capacitor CST and thin film transistor (not shown) thereon, an upper substrate 13, and a liquid crystal layer 12 with dielectric anisotropy interposed between the lower substrate 11 and the upper substrate 13. A color filter 14 is disposed on the upper substrate 13. The micro-reflective transmission display 100 can provide a reflective image due to reflection of the ambient light from the backlight unit (BLU) 15.
FIG. 2 is a block diagram of a conventional micro-reflective transmission LCD. The micro-reflective transmission display LCD 100 comprises an LC panel assembly 30, a gate driver 40 and a data driver 50 which are connected to the panel assembly 30, and a signal controller (not shown) controlling the desired elements.
The LC panel assembly 30, in the structural view shown in FIG. 1B, includes a lower substrate 11, an upper substrate 13 and a liquid crystal layer 12 interposed therebetween. The LC panel includes a plurality of display signal lines Gl-Gn and Dl-Dm and a plurality of pixels connected thereto and arranged substantially in a matrix as shown in circuital view of FIG. 1A.
The display signal lines Gl-Gn and Dl-Dm are provided on the lower substrate 11 and comprise a plurality of gate lines Gl-Gn transmitting gate signals (called scanning signals) and a plurality of data lines Dl-Dm transmitting data signals. The gate lines Gl-Gn extend substantially in a row direction and are substantially parallel to each other, while the data lines Dl-Dm extend substantially in a column direction and are substantially parallel to each other.
Each pixel includes a switching element T connected to the display signal lines Gl-Gn and Dl-Dm and an LC capacitor CLC and a storage capacitor CST that are connected to the switching element T. The switching element T such as a TFT is provided on the lower substrate 11 and has three terminals: a control terminal connected to one of the gate lines Gl-Gn; an input terminal connected to one of the data lines Dl-Dm and an output terminal connected to the LC capacitor CLC and the storage capacitor CST.
The storage capacitor CST is an auxiliary capacitor for the LC capacitor CLC. The storage capacitor CST is supplied with a predetermined voltage such as the common voltage Vcom.
The conventional transmissive LCD 10 with four color RGBW pixels, however, may have other difficulties. For example, the four color liquid crystal display applied as a micro-reflective transmission display requires improving both reflectance and reflective contrast ratio (CR). For micro-reflective transmission LCDS, reflection from back light unit (BLU) is defined as external reflection, while reflection from electrodes of storage capacitor CST or metal signal and data lines is defined as internal reflection. The internal reflection can cause noise in micro-reflective transmission LCDS, thus the reflective contrast ratio (CR) is reduced. As such, the storage capacitor CST corresponding to each pixel reflects the ambient light internally, as indicated in LR. Since internal reflection LRW in the white sub-pixel WP lacks color filter blocking, both internal and external reflection in the white sub-pixel WP may deteriorate reflective quality noise such that the conventional four color liquid crystal display cannot attain the desired reflective image quality due to deteriorated reflective contrast ratio (CR).